Electroplating process and apparatus



Nov. 29, 1960 L. K. KOSOWSKY 2,962,427

ELECTROPLATING PROCESS AND APPARATUS Filed June 28, 1957 INVENTOR. LEOK. KOSOWSKY his ATTORNEYS.

ELECTROPLATING PROCESS AND APPARATUS Leo K. Kosowsky, Bridgeport, Conn.,assignor toCo=- lnmbia Broadcasting System, Inc., New York, N.Y., acorporation of New York Filed June 28, 1957, Ser. No. 668,666

6 Claims. (Cl. 204-34) The present invention pertains to anelectroplating process and apparatus, and more particularly to a processand apparatus for the cathodic etching and copper striking of stainlesssteel articles.

Heretofore, in the electroplating of metallic articles with a metalliccoating it has been the practice to remove the grease and dirt adheringto the article by treating the article with a conventional degreasingsolution. The surface of the article may then be roughened, for example,by making it the anode in an electrolytic solution. The article is thenmade the cathode in an etch solution to further prepare the surface ofthe article for the metallic coating by etching the article and forminga film of nascent hydrogen thereon. After the cathodic etching of thearticle, it is transferred from the etch solution and immersed in astrike solution wherein it is also made the cathode in order to form astrike coating thereon. After the preliminary strike or flash coating isapplied to the article, it is transferred to an electroforming unitwherein the article'is again made the cathode in order to apply thereonthe final metallic coating.

This present practice in regard to the electroplating of articles with ametallic coating suffers from the very serious drawback in that duringthe step of transferring the article from the cathodic etch solution tothe strike solution, the film of hydrogen thereon is dissipated. Sincethis film of hydrogen is necessary in order to obtain a strong, firmlybonded strike coating, the dissipation of the hydrogen film is highlydisadvantageous and presents a considerable problem to theelectroplating industry.

It is, therefore, the object of the present invention to provide anelectroplating process and apparatus in which there is no loss of thehydrogen film formed on the article by the cathodic etching of thearticle and which accordingly makes it possible for the first time toproduce a strong adherent strike coating upon an article.

In the drawing, there is shown a perspective view partly in section ofan embodiment of the apparatus of the invention.

In general, the process of the invention comprises treating an articlein an etch solution while the article is a cathode to form thereon ahydrogen film. The etch solution is then displaced with a solution ofthe metal ions which are to form the strike coating while the flow ofcurrent is continued at a lower voltage and current density. While theetch solution is being displaced by the strike solution and afterdisplacement thereof, the cathodic article is struck with the desiredmetallic coating.

In particular, the process of the present invention comprises etching anarticle, such as a stainless steel article formed from the well knowniron-chromium alloy, with an etch solution, such as a sulfuric acidsolution, while the article is a cathode. The etch solution is thendisplaced upwardly from its container by a strike solution, such as anaqueous solution of copper sulfate, whose minimum specific gravity isgreater than the maximum specific gravity of the etch solution. Duringthe displacement of the etch solution by the strike solution the currentdensity and voltage are lowered, but the flow of current is continued sothat the lower portion of the article is being struck with the metalliccoating while the upper portion of the article is being etched by theetch solution and is having a hydrogen film formed thereon due to thestratification of the two solutions. After the etch solution has beencompletely displaced by the strike solution, the flow of current iscontinued at the lower current density so that the cathodic article isstruck with the metal ions present in the strike solution. Accordingly,during the process there is no dissipation of the hy-, drogen film onthe article between the etching step and the striking step.

Turning now to the apparatus of the invention, it com prises in generala tank having at least three compartments. Overflow means are providedto connect two of the compartments to one another. Means are alsoprovided for transferring fluids from one compartment to another.

In particular, the apparatus of the invention comprises an acidresistant tank subdivided into three compartments by two partitions. Oneof these partitions extends from the base of the tank to the top of thetank while the second partition extends from the base of the tank butterminates below the top of the tank so that fluid may over:

flow from one compartment to the other over the lower partition. Thecenter compartment is provided with at least one anode, such as a leadanode, and with the article to be etched and struck which is made thecathode. Each of the three compartments are connected one to the otherby means for transferring fluids from one compartment to the other whichmeans are a system of pipes, valves, and a pump driven by a motor sothat by opening and closing valves fluids may be pumped from onecompartment to another as desired.

Referring now to the drawing, the apparatus of the invention comprisesan elongated rectangular acid resistant tank 1 having end walls 2 and 3and side walls 4 and 5 all connected to a base 6. The tank 1 issubdivided into three compartments A, B, and C by partitions 7 and 8.Partition 7 between compartments A and B extends from the base 6 to thetop of side walls 4 and 5, while partition 8 between compartments B andC also extends upwardly from the base 6 but terminates below the top ofside walls 4 and 5, Le, partition 8 has a height less than that ofpartition 7.

The center compartment B is provided with one or more lead anodes 9connected by a positive lead 11 to a source of electricity and with anarticle 28 to be plated which serves as the cathode and is alsoconnected to the same source of electricity by negative lead 10.

Compartments A, B, and C have connected to the bottoms thereof lines 12,13, and 14 respectively which lines are all connected to an inputmanifold 15 running to the intake side of a pump P driven by a motor M.The out-' put side of pump P is connected to an output manifold 16 whichis joined to each of lines 12, 13 and 14 by feed lines 17, 18 and 19respectively.

Line 12 is provided with a valve 20 interposed therein between feed line17 and input manifold 15. Line 13 is provided with a valve 21 interposedbetween feed line 18 and the input manifold 15. Line 14 is provided witha valve 22 interposed between feed line 19 and input manifold 15. Feedlines 18 and 19 are provided with valves 23 and 24 respectively. Outputmanifold 16 is pro vided with a valve 25 interposed between feed lines17'- In the operation of the apparatus, end compartment A Patented Nov.29, 1960 of tank 1 is filled with an aqueous strike solution of coppersulfate having a minimum specific gravity of 21 Baum. The centercompartment B of tank 1 is filled with a 20% etch solution of sulfuricacid whose maximum specific gravity is 16 Baum, i.e., the copper sulfatestrike solution in compartment A has a specific gravity greater than thespecific gravity of the sulfuric acid etch solution in compartment B.Compartment C of tank 1 is empty and all six valves 20 through 25 areclosed so that there is no flow of fluids through any of the lines 12through 19.

The lead anode 9 is immersed in the sulfuric acid etch solution incompartment B and so is the stainless steel article 28 which is made thecathode. A current density of approximately 200 to 250 amperes persquare foot is applied to the cathodic stainless steel article 28 tocause the cathodic etching thereof and to form thereon a film.

of hydrogen.

After the elapsed etching time, the voltage is dropped to 1% to 2 volts.Valves 20 and 23 are then opened and the motor M started to drive pump Pand transfer the copper sulfate strike solution from compartment A tocompartment B via line 12, valve 20, input manifold 15, pump P, outputmanifold 16, feed line 18, valve 23, and line 13'. The copper sulfatestrike solution entering the base of'comp-artment B is deflected bybaflle plate 26 so as not to agitate the sulfuric acid etch solution incompartment B. The continued flow of the heavier copper sulfate strikesolution into compartment B upwardly displaces the sulfuric acid etchsolution therefrom and causes the sulfuric acid etch solution tooverflow from compartment B over the top of lower partition 8 and intoempty compartment C. After the sulfuric acid etch solution has beencompletely displaced from compartment B into compartment C by theheavier copper sulfate strike solution, valves 20 and 23 are closed andthe motor M and pump P stopped. The flow of electric current iscontinued until the desired thickness of the copper strike coating hasbeen applied to article 28.

In this manner, the hydrogen film formed on the stainless steel article28 during the cathodic etching is not dissipated prior to the strikingof the article 28 with the copper sulfate strike solution and "hence astrong, firmly bonded strike coating of copper is applied to thestainless steel article 28. After suitable elapsed time for copperstriking, stainless steel article 28 is removed from compartment 'B andtransferred to an electroforming unit wherein the final copper coatingis applied thereto.

The copper sulfate strike solution in compartment B is returned tocompartment A by opening valves 21 and 25 and starting motor M to drivepump P. The copper sulfate strike solution in compartment B flows tocompartment A via line 13, valve 21, input manifold 15, pump P, outputmanifold 16, valve 25, feed line 17, and line 12.

After the copper sulfate strike solution has been emptied fromcompartment B and returned to compartment A, valves 21 and 25 are closedand valves 22 and 23 opened in order to return the sulfuric acid etchsolution from compartment C to compartment B. The sulfuric acid etchsolution is returned from compartment C to compartment B via line 14,valve 22, input manifold 15, pump P, output manifold 16, valve 23, feedline 18, and line 13. When the sulfuric acid etch solution has beenemptied from compartment C and returned to cornpartment B, the motor Mand pump P are stopped and valves 22 and 23 are closed.

After the purification of the copper sulfate strike solution now incompartment A and the sulfuric acid etch solution now in compartment B,the apparatus is ready for use again.

It will be appreciated in view of the above discussion that theinvention provides a process and apparatus Wherein an article may becathodically etched and have formed thereon a film of hydrogen whichfilm is not dissipated prior to plating the article with a metallicstrike coating because the article to be struck is first immersedcompletely in an etch solution, then the upper portion of the articleremains immersed in the etch solution while the lower portion thereof isprogressively immersed in a strike solution, and subsequently thearticle is completely immersed in a strike solution due to the upwarddisplacement of the etch solution by the heavier strike solution. Theinvention, therefore, provides means for procuring a strong, firmlybonded strike or flash coating of metal upon an article.

It will be further appreciated that the apparatus of the invention maytake many forms other than the preferred embodiment illustrated in thedrawing. Thus, the apparatus may comprise several parallel tanks 1 andmay contain one or more anodes and cathodes within compartment B.Furthermore, the tank 1 may be subdivided into more than threecompartments, if desired. Moreover, the cathode and anode need not beplaced in compartment B, but they could be placed in any of the threecompartments and suitable means, such as piping and valves, provided forthe overflow of the etch solution and the transfer of fluids from onecompartment to the other. For example, the anode and cathode can beplaced in com-partment C containing an etch solution while compartment Acontains a strike solution and compartment B is empty. The etch solutionin compartment C can then be caused to overflow over partition 8 intocompartment B by displacement thereof with the strike solution incompartment A entering into the base of compartment C.

Furthermore, the process of the invention need not be restricted to thecopper striking of a stainless steel article by using a copper sulfatestrike solution. Other suitable strike solutions, such as coppercyanide, can be used equally as well. In addition, the process of theinvention need not be restricted to the copper striking of stainlesssteel articles, but it may be applied in general to the striking of anymetallic article with any desired metallic coating, provided, of course,the process is capable of being performed electrolytically.

Many other variations and modifications in the process and apparatus ofthe invention will be readily apparent to those skilled in the art.Accordingly the process and apparatus of the invention are to be limitedonly within the scope of the appended claims.

I claim:

1. An electroplating process comprising etching a stainless steelarticle in a sulfuric acid etch solution in an electroplating tank Whilethe article is a cathode, upwardly displacing the sulfuric acid etchsolution from said tank by flowing into said tank a strike solutioncontaining copper ions and having a specific gravity greater than thespecific gravity of the sulfuric acid solution, and striking thecathodic article with the copper ions.

2. An electroplating process comprising etching a stainless steelarticle in a sulfuric acid etch solution in an electroplating tank whilethe article is a cathode, upwardly displacing the sulfuric acid etchsolution from said tank by flowing into said tank a copper sulfatestrike solution having a specific gravity greater than the specificgravity of the sulfuric acid solution, and striking the cathodic articlewith copper ions.

3. An electroplating process comprising immersing a stainless steelarticle in a sulfuric acid etch solution in an electroplating tank whilethe article is a cathode to etch the stainless steel article and formthereon a film of hydrogen, upwardlydisplacing the sulfuric acid etchsolution from said tank by flowing into said tank a solution of coppersulfate having a specific gravity greater than the specific gravity ofthe sulfuric acid solution while continuing the flow of electric currentat a reduced current density, and plating the cathodic stainless articlewith a strike coating of copper.

4. An electroplating apparatus consisting essentially of a tank; twopartitions in the tank subdividing the tank into a strike solutionsupply compartment, an etch solution compartment, and an overflowcompartment, the partition separating the etch solution compartment fromthe overflow compartment having a height less than that of the otherpartition to form the sole overflow means; a pump connected to an inputmanifold and an output manifold, said input manifold being connected bybase lines to the base of each compartment and said output manifoldbeing connected by feed lines to each of said base lines; and a valve ineach of said base and feed lines; whereby etch solution in the etchsolution compartment can overflow the lower partition into the overflowcompartment by the upward displacement thereof of heavier strikesolution pumped from the strike solution supply compartment and wherebyboth solutions can be subsequently pumped back sequentially to theiroriginal compartments.

6 5. The apparatus of claim 4 containing a cathode and an anode withinsaid etch solution compartment.

6. The apparatus of claim 4 having a baffle plate over the outlet of thebase line connected to the base of the etch solution compartment.

References Cited in the file of this patent UNITED STATES PATENTS2,093,238 Domm Sept. 14, 1937 2,285,548 Wesley June 9, 1942 2,363,973Kennedy et al Nov. 28, 1944 2,519,945 Twele et al. Aug. 22, 19502,560,966 Lee July 17, 1951 2,721,562 Irvine Oct. 25, 1955 2,762,763Kenmore Sept. 11, 1956 FOREIGN PATENTS 733,110 Great Britain July 6,1955 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No,2362, 127 November 29, 1960 Leo K. Kosowsky ears in the above numberedpat- It is hereby certified that error afip :5 Patent should read as entrequiring correction and that the said Letter corrected below.

Column 4, line 74, after "'stain lese" insert steel Signed and sealedthis 9th day of May 1961.

(SEAL) Attest: DAVID L40 LADD ERNEST we SWIDER I v I Attesting OfficerCommissioner of Patents

1. AN ELECTROPLATING PROCESS COMPRISING ETCHING A STAINLESS STEELARTICLE IN A SULFURIC ACID ETCH SOLUTION IN AN ELECTROPLATING TANK WHILETHE ARTICLE IS A CATHODE, UPWARDLY DISPLACING THE SULFURIC ACID ETCHSOLUTION FROM SAID TANK BY FLOWING INTO SAID TANK A STRIKE SOLUTIONCONTAINING COPPER IONS AND HAVING A SPECIFIC GRAVITY GREATER THAN